1. Field of the Invention
The present invention relates to an adhesive. More particularly, it relates to a two-part adhesive having water incorporated.
2. Discussion of Background
There is an increasing demand for adhesives which can be cured in a short period of time at room temperature, from the viewpoint of energy saving, labor saving, saving of resources, etc.
Heretofore, as room temperature quick-curing adhesives, a two-part type quick-curing epoxy adhesive, an anaerobic adhesive, an .alpha.-cyanoacrylate adhesive and a second generation acrylic adhesive (SGA) have been known.
The two-part type quick-curing epoxy adhesive is designed to be used in such a manner that a main agent and a curing agent are measured, mixed and coated on an object to be bonded, whereupon the main agent and the main components of the curing agent will react for curing. If the measurement and mixing of the main agent and the curing agent are inadequate, the two-part type quick-curing epoxy adhesive tends to undergo a substantial deterioration in the strength. Further, even if the measurement and mixing are conducted adequately, it still has a drawback that it is poor in the peel strength and impact strength.
The above-mentioned anaerobic adhesive is cured by shutting off air by pressing the adhesive composition between the objects to be bonded. Therefore, at the time of bonding, the adhesive is likely to be pressed out from the objects, and the adhesive at the portion which is in contact with air, will not be cured. Further, it has a drawback that it will not be cured also in a case where the clearance between the objects to be bonded, is large.
The above-mentioned .alpha.-cyanoacrylate adhesive provides excellent operation efficiency, but it has low peel strength and impact strength and is poor in the moisture resistance and water resistance. Thus, it has a disadvantage that its useful range is very much limited.
The above-mentioned second generation acrylic adhesive (SGA) is a two-part type. However, it has excellent operation efficiency in that it is unnecessary to accurately measure the two liquids, and it is capable of being cured quickly in from a few minutes to a few tens minutes by extremely rough measurement and mixing (in some cases, merely by contacting the two liquids). Yet, it provides high peel strength and impact strength, and curing of the portion pressed out of the objects to be bonded, is excellent. Therefore, an adhesive of this type has been widely used.
Such SGA is disclosed in e.g. U.S. Pat. Nos. 3,890,407 and 4,096,201. However, it has a drawback that it does not provide adequate adhesiveness to a metal object.
With respect to improvement of the adhesiveness of SGA to a metal, U.S. Pat. Nos. 4,233,115 and 4,452,944 and Japanese Unexamined Patent Publication No. 84964/1984 disclose that the adhesiveness to a metal object can be improved by an addition of a monomer of a phosphoric acid ester type. However, even such improvement is not yet adequate with respect to the improvement of the adhesiveness to iron or stainless steel, and it has been found that the adhesiveness to such a metal object tends to be poor, and the bond strength tends to deteriorate.